Physics for IGCSE & O level - Waves And Sounds (Section 7 - No. 16)
What will happen to the frequency of a wave if the wavelength doubles (assuming the speed remains constant)?
The frequency will double.
The frequency will halve.
The frequency will stay the same.
The frequency will become zero.
Explication
If the wavelength doubles and speed is constant, the frequency must halve (Speed = Frequency x Wavelength).